The long term goal of this project is to identify the gene responsible for Niemann-Pick Type C (NP-C) and to study its role in the pathogenesis of the disorder. NP-C is an autosomal-recessive, neurovisceral lipid storage disorder and presents as variable hepatosplenomegaly, vertical supranuclear ophthalmoplegia, progressive ataxia, dystonia, and dementia. The primary molecular defect in NP-C has not been identified, however the human disorder has been mapped to a 2 cM region on 18q11. This proposal will use the mouse model of NP-C (m-npc) to expedite the isolation of the gene responsible for this devastating disorder. The mouse project will integrate extensively with the human NP-C positional cloning project currently in progress at the NIH and will consist of three phases. First, a 0.1cM mouse genetic linkage map will be generated in the region containing m-npc using a series of intersubspecific mouse backcrosses. To date we have narrow the m-npc locus to a 2cM interval (400 meioses). In the second phase, the murine genetic map will be integrated with the human genetic and physical maps using cloned DNA fragments generated from the contig of human DNA containing the NP-C gene. We have already identified two polymorphic markers that link the mouse and human maps and these are being typed on our backcross progeny. Integration will further narrow the region that must contain the gene. The third phase will involve evaluating genes as candidates for NP-C from a pool of cDNA clones and trapped exon fragments that will be isolated from the human physical contig. Genes will be assessed by Northern blot, Southern blot, SSCP and sequencing analyses using samples isolated from spontaneous mouse mutants in comparison to their isogenic wild type controls. Three genes are currently being tested as candidates for NPC.